01 - Place chicken breasts in the bottom of the slow cooker. Season evenly with salt, black pepper, and dried Italian herbs.
02 - Scatter the chopped onion and minced garlic over the seasoned chicken.
03 - Pour the chicken broth and heavy cream evenly over the ingredients in the slow cooker.
04 - Distribute the cream cheese cubes and butter across the top of the mixture.
05 - Cover and cook on low setting for 4 hours, or until chicken reaches an internal temperature of 165°F and is tender.
06 - Remove the cooked chicken breasts and shred using two forks. Return the shredded chicken to the slow cooker.
07 - Add the uncooked fettuccine to the slow cooker, stirring to submerge the pasta completely in the sauce.
08 - Sprinkle the freshly grated Parmesan cheese over the mixture and stir well to combine.
09 - Cover and cook on high setting for 25-35 minutes, stirring once or twice, until pasta is al dente and sauce has thickened to a creamy consistency.
10 - Serve immediately, garnished with chopped fresh parsley.